Method of forming and assembly of parts

ABSTRACT

A method of assembling two or more parts together that may be metal, ceramic, metal and ceramic parts, or parts that have different CTE. Individual parts are formed and sintered from particles that leave a network of interconnecting porosity in each sintered part. The separate parts are assembled together and then a fill material is infiltrated into the assembled, sintered parts using a method such as capillary action, gravity, and/or pressure. The assembly is then cured to yield a bonded and fully or near-fully dense part that has the desired physical and mechanical properties for the part&#39;s intended purpose. Structural strength may be added to the parts by the inclusion of fibrous materials.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention is generally related to the assembly of parts and moreparticularly to the forming and assembly of at least two metal and/orceramic parts or parts that have different coefficients of thermalexpansion.

2. General Background

In the present state of the art, various “3-D printers” use a processthat makes parts by spraying glue down and sprinkling metal powder intothe glue. The part is built up in layers to form a three-dimensionalpart which is baked to remove the glue and then sintered to form astructural part. A part formed in this manner is not fully dense(approximately 60% open and 40% dense) at this point in the process andhas a very irregular surface, with open and interconnecting porosity.The part is then placed in a container holding a molten metal that has alower melting point. The part draws the melted metal into the part bywicking and capillary action. The metal drawn into the part is thenallowed to solidify.

The present state of the art is limited to forming a single part frommetal and does not adequately address the assembly of two or more partsin any form or the assembly of parts that have different coefficients ofthermal expansion (CTE). One important deficiency in the present stateof the art is the inability to assemble two or more parts together toproduce a single part that does not result in typical problems ofreduced strength at the bond area between the original parts. Theseproblems at the bond area are exacerbated where manufacturingrequirements or limitations present the situation where two or moresmall parts must be combined to produce a single larger part having thesame physical properties, such as strength and flexibility, as each ofthe individual smaller parts. Parts having different CTE present specialdifficulties and needs when being assembled together. If the means usedto bind the parts together cannot accommodate the different CTE, theconnection between the two parts may break or either one or both of theparts may break during heating or cooling.

SUMMARY OF THE INVENTION

The invention addresses the above needs. What is provided is a method ofassembling two or more parts together that may be metal, ceramic, metaland ceramic parts, or parts of various materials that have differentCTE. Individual parts are formed and sintered to increase theirstructural integrity from particles or other materials in a manner thatleaves a network of interconnecting porosity in each sintered part.Alternatively, the parts need not be sintered if they consist ofperforated metal and/or perforated ceramic parts, or if they consist ofmetal foam or ceramic foam having the proper amount of open andinterconnecting porosity. Both sintered and non-sintered parts mayoptionally incorporate fiber materials between the parts to form alaminate or incorporate fiber materials by wrapping the fiber materialsaround the parts in order to increase the structural strength of thepart. Typically, the separate parts are assembled together and then afill material is infiltrated into the assembled parts. The infiltratedassembly is then cured to yield a strongly bonded part that hassufficient physical and mechanical properties for its intended purpose.

BRIEF DESCRIPTION OF THE DRAWINGS

For a further understanding of the nature and objects of the presentinvention reference should be made to the following description, takenin conjunction with the accompanying drawings which are not to scale andin which like parts are given like reference numerals, and wherein:

FIG. 1 is a pressed “green” metal or ceramic part.

FIG. 2 is an enlarged view of an indicated section of FIG. 1.

FIG. 3 is the same part as in FIG. 1 after sintering.

FIG. 4 is an enlarged view of an indicated section of FIG. 3.

FIG. 5 is a sectional view that illustrates an example of the use of theinvention.

FIG. 6 and 7 are section views that illustrate the use of the inventionwith a fiber reinforcing material between the parts.

FIG. 8 and 9 are section views that illustrate the use of the inventionwith a fiber reinforcing material wrapped around the parts.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The forming and assembly method is generally comprised of the followingsteps. Appropriate materials are formed into at least two separate partsin a manner that leaves a network of interconnecting porosity in eachpart. Each of the formed parts is then sintered such that each of thesintered parts continues to maintain a network of interconnectingporosity. Sintering is accomplished by heating the green part using anyheating method suitable for sintering such as microwave energy,infrared, induction, kiln, furnace, or any other appropriate heatingmethod until the particles of the pressed material fuse at the points ofcontact. The fusing creates a typical neck type structure or bondbetween adjacent particles. Sintering yields a much stronger part incomparison to a part that is not sintered. The sintered parts are thenassembled together, after which a fill material is infiltrated into theassembled parts. The infiltrated assembled parts and fill material arethen cured.

The fill material must be in liquid form at the time of its infiltrationinto the assembled parts. Fill material that must be melted prior toinfiltration should have a melting point sufficiently less than themelting point of the material used to form the sintered parts so as tomaintain the structural integrity of the assembled parts; typically, themelting point of the fill material is about two thirds of the meltingpoint of the material used to form the sintered parts. If a melting stepis required, the fill material may be heated by the use of microwaveenergy, infrared, induction, kiln, furnace or any other appropriatetraditional heating methods.

The liquid fill material may be infiltrated into the assembled parts invarious ways. For example, it may drip into the assembled parts bygravity feed if the fill material is placed above the assembled parts.It may be forced into the assembled parts under pressure. Alternatively,the liquid fill material may be drawn into the assembled parts bywicking or capillary action, or infiltrate the assembled parts in otherways. In cases where the liquid fill material does not naturally possessa property that will cause it to readily wet and wick into the sinteredparts, a wetting or fluxing agent may be added to the fill material.

Curing the infiltrated assembled parts and fill material is accomplishedin a manner consistent with the properties of the fill material. Forexample, metals and ceramics cure by solidifying. Polymers cure bypolymerizing. Thermosets cure by setting up. Curing results in theformation of a chemical or mechanical bond in the infiltrate andsometimes between the infiltrate and assembled part.

The properties of the parts being formed, sintered and assembled can beselected by choosing the appropriate materials to form and densify theparts. These properties, which can be affected by the proper choice ofmaterials include, but are not limited to, corrosion resistance,ductility, modulus, hardness, wear resistance, and lubricity. If metalor ceramic material is used for the parts, the fill material must havematerial compatibility with the metal or ceramic. These parts may becomprised of sintered metal and ceramic parts, metal and ceramic foamparts, perforated metal and ceramic parts, reinforcing fibers, orsimilar components, provided they have open interconnecting porosity orvoids to allow the fill material to infiltrate the parts.

The method of the invention may also be applied to the assembly of metalfoam, ceramic foam, perforated metal, and perforated ceramic parts thathave the desired amount of open and interconnecting porosity. For thesetypes of parts, sintering is not necessary. The parts are formed,assembled, infiltrated with the fill material, and the parts and fillmaterial are then cured.

If greater structural strength is desired for the assembled part, anadditional step of placing a structural fiber (fiber reinforcingmaterial) (such as carbon, boron, or Kevlar® synthetic fiber) betweenthe parts may be performed prior to infiltrating the material. Forexample, carbon fiber layers may be placed between alternating metal andceramic sheets, as in the case of a laminated armor plate.

Alternatively, the additional step may be performed by wrapping at leasta portion, or all, of the assembled parts with a fiber reinforcingmaterial and then infiltrating the fiber reinforcing material andassembled parts with fill material.

For example, carbon fiber could be wrapped around a sintered metal orceramic cylinder and then infiltrating the fill material. If necessary,the fiber reinforcing material may be placed between the parts and atleast partially wrapped around the parts.

One embodiment of the invention is described in the following way. Usingpowdered metals and/or ceramics that have the desired properties,individual parts are formed from particles using powder metallurgyand/or ceramic forming techniques that leave a network ofinterconnecting porosity in each part. A green pressed part 10 isillustrated schematically in FIG. 1. FIG. 2 is an enlarged view ofindicated section 2 of FIG. 1 that illustrates the particles 12 that arepressed to form the part 10. It can be seen that the particles toucheach other while leaving an open interconnecting porosity between them.

Each part is then sintered, with the sintering processing resulting in apart preferably having approximately forty percent density and beingapproximately sixty percent open (typical). A sintered part 14 isillustrated schematically in FIG. 3. FIG. 4 is an enlarged view ofindicated section 4 of FIG. 3 that illustrates particles 12 after theyhave been sintered to become sintered particles 12A. The sinteredparticles 12A are fused together, with the drawing illustrating thetypical neck structure 16 of the fusing bond. It can be seen that thesintered particles 12A still leave the open interconnecting porositybetween the particles, which provides space for a fill material.

Two or more separate sintered parts are assembled together and placed ina tray containing a selected molten fill material. The fill material hasa melting point that is preferably no more than two thirds (typical) ofthe melting point of the material used to form the sintered parts. Theentire assembly is heated and the molten fill material is drawn into theassembled sintered parts by wicking or capillary action. The assembly isthen cured by cooling it until it solidifies. This method produces asingle assembled part (from the previous two or more parts). Theresulting part is fully or near-fully densified and bonded together in asingle operation.

The inventive method provides several advantages as described below.

The method preserves the net shape capabilities of the powder metallurgyprocess for producing a green pressed part while yielding a bonded andfully or near-fully dense part.

The method can be used to manufacture net-shaped and near-net-shapedparts in various materials (ceramic, metals, and other materials) and toassemble and bond the parts together in a simple process with a greatreduction of time and expense.

The method allows parts of many dissimilar materials with differentproperties to be easily assembled and bonded. As an example, partshaving different CTE (coefficients of thermal expansion) can be joinedtogether without the inherent bond weaknesses typically encountered withother joining methods for parts having different CTE. The flow of thefill material between the parts results in a bond that eliminates thetypical problems of weakness, limited number of thermal cycles, andbreakage typically encountered when joining parts having different CTE.

The method is suitable in the production of specialized parts. As anexample, where a portion of an engine block does not need the strengthof a solid metal piece, a void can be engineered into the engine blockto reduce weight. One way to accomplish this is to form and sinter afirst engine block part that has one side open to create the void. Asecond engine block part is formed and sintered that is designed to fitover the opening of the first part as a lid to seal shut the void.

The second part is then assembled to the first part. The assembled partsare placed in a tray holding the molten fill material. The fill materialis caused to wick into the assembled parts as described above. Thisprocess completely attaches and bonds the first and second partstogether with an engineered void. There is no weakness at the bond inthe final part that would normally result from using existingmanufacturing methods.

The method reduces the number of steps normally required in this type ofmanufacturing.

The method results in a bonded region between two parts that isinherently free from porosity and buildup of contaminants and otherproblems that plague the bonded region created when using existing hightemperature joining processes.

The method tends to draw the assembled parts tighter together. Thisphenomenon results from the fill material that forms the bond beinginfiltrated through the part as the bond is being formed and from thecuring step.

The method provides for the fill material to flow through the interfaceof the two parts to be joined and into the bulk area of the part. Thisdiffers significantly from oven brazing or other traditional methods ofjoining parts, which occurs only at the interface of the two parts. Thissignificant difference can be appreciated by imagining the taking of atransverse slice of the interface region and viewing it as a horizontalcut. The view of the joined region using the inventive method wouldappear as one single part without an interface, whereas the view of thejoined region using brazing or other traditional method would appear asthree distinct sections (two parts and a joint sandwiched between them).

The method can be used to improve the bonding characteristics of metalsand ceramics and can produce a finished product with the combinedbenefits of both materials while reducing the number of steps requiredin comparison with traditional manufacturing processes. Some of theunique aspects of the method are: 1) the ability to take parts withdifferent properties and characteristics and assemble them by flowing afill material through them; 2) the bonding of ceramics and metals bycreating a cermet bonded to a metal; 3) the method increases the surfacearea and bond quality between two parts; and 4) making precision-formedand sintered parts and simultaneously bonding and densifying them tocreate a net-shaped finished product.

The method of the invention may also be useful to utilize the elementalcomponents of an alloy. An example is nickel-aluminum-bronze alloy whichis used in applications where corrosion resistance is important. Tomanufacture an assembly using such material, the elemental components ofthe alloy (nickel, aluminum, copper, and iron, in this case) aresegregated into 1) an alloy-proportionate quantity of those elementsthat raise the eutectic melting point of the alloy and 2) analloy-proportionate quantity of those elements that lower the alloy'seutectic melting point. Those elements that raise the eutectic meltingpoint (nickel 5.5 wt % of total, iron 5 wt % of total, and copper 29.5wt % of total melt point ˜1400 C.) are sintered into a porous powderedmetal body. The other elements (copper 45 wt % of total, and aluminum 15wt % of total, melt point ˜925 C.) are then melted and allowed toinfiltrate into the porous metal body formed fromnickel/iron/copper/aluminum. By holding the temperature of the assemblyat elevated temperature, the fill material (with a lower melting point)actually diffuses into the surface of the sintered parts, creating thedesired alloy for some depth in the part. If allowed to continue forvery long heating periods, the entire structure would becomehomogeneously alloyed (the diffusion process is controlled by Ficks LawEquations). However, much of the benefit of the alloy can be achievedmuch more economically by only heating long enough to achieve a desireddegree of diffusion (alloying).

The use of materials other than metal as the fill material, such as anepoxy or thermoset, to join the sintered materials would facilitate theease of room temperature assembling and joining while still achievinggood bond strength because of the excellent mechanical and physical bondand great amount of bonding surface area. As stated, the fill materialneed not be an epoxy or thermoset to realize the benefits of theinventive method.

Hydroxyapatite is an example of a fill material that is not a metal,epoxy, or thermoset. The following is an example of using hydoxyapatiteas a fill material in a medical application. Sintered titanium metalparts incorporated with a hydroxyapatite fill material could be used formedical implants. Hydroxyapatite is a biomaterial that is able to bondchemically to bone. Thus, this would encourage good osteogenic boneattachment to the medical implant. Using this approach, it would bepossible to functionalize the surface of such an implant with aphoto-polymerizable fill material and make an immediate bond to bone byultraviolet (UV) curing. This temporary bond of bone-to-implant could bereplaced by a permanent mechanical bond as the osteogenic bone growthpenetrated the temporary interface.

FIG. 5 illustrates the use of the invention wherein a sintered powdermetal part 18 and porous part 20 have been infiltrated with a selectedmetal 22. The porous part 20 is intended to be generally representativeof parts formed from metal foam, ceramic foam, perforated metal, orperforated ceramic.

FIG. 6 illustrates the use of the invention wherein a fiber reinforcingmaterial 26 has been placed between the two parts 24. FIG. 7 illustratesthe two sintered metal powder parts 24 after they have been assembledand infiltrated with a selected metal 28.

FIG. 8 illustrates the use of the invention wherein two parts 32 havebeen wrapped with a fiber reinforcing material 34. FIG. 9 illustratesthe two parts 30 infiltrated with a selected metal 36.

It should be understood that a solid or dotted line is shown in the FIG.5 described above only for ease of illustrating the separately formedparts and that, as described above, infiltration of the fill materialwill effectively cause a cross section of the assembled and bonded partsto appear as one.

Because many varying and differing embodiments may be made within thescope of the inventive concept herein taught and because manymodifications may be made in the embodiment herein detailed inaccordance with the descriptive requirement of the law, it is to beunderstood that the details herein are to be interpreted as illustrativeand not in a limiting sense.

1. A method of forming and assembling at least two parts together,comprising the steps: a. forming at least two separate parts in a mannerthat leaves a network of interconnecting porosity in each part; b.sintering each formed part; c. assembling the sintered parts together;d. causing a fill material to be infiltrated into the assembled parts;and e. curing the parts and fill material.
 2. The method of claim 1,wherein said parts are formed using powder metallurgy and/or ceramicforming techniques.
 3. The method of claim 1, wherein the fill materialis a molten metal.
 4. The method of claim 1, wherein the fill materialis an epoxy.
 5. The method of claim 1, wherein the fill material is athermoset.
 6. The method of claim 1, wherein the separate parts aremetal and ceramic.
 7. The method of claim 1, wherein the separate partsare metal or ceramic.
 8. The method of claim 1, wherein the separateparts have different coefficients of thermal expansion.
 9. The method ofclaim 1, further comprising placing a fiber reinforcing material betweenthe sintered parts during the step of assembling the sintered parts. 10.The method of claim 1, further comprising wrapping at least a portion ofthe assembled parts with a fiber reinforcing material before the step ofinfiltrating the fill material.
 11. The method of claim 1, wherein theseparate parts are formed from titanium.
 12. The method of claim 11,wherein the fill material is a biomaterial capable of bonding to bone.13. A method of forming and assembling metal and ceramic parts,comprising the steps: a. forming at least two parts using powdermetallurgy and/or ceramic forming techniques in a manner that leaves anetwork of interconnecting porosity in each part, said parts beingseparate metal and ceramic parts; b. sintering each formed part; c.assembling the sintered parts together; d. causing a fill material to beinfiltrated into the assembled parts; and e. curing the parts and fillmaterial.
 14. The method of claim 13, wherein the fill material ismolten metal.
 15. The method of claim 13, wherein the fill material isepoxy.
 16. The method of claim 13, wherein the fill material is athermoset.
 17. The method of claim 13, wherein the separate parts havedifferent coefficients of thermal expansion.
 18. The method of claim 13,further comprising placing a fiber reinforcing material between thesintered parts during the step of assembling the sintered parts.
 19. Themethod of claim 13, further comprising wrapping at least a portion ofthe assembled parts with a fiber reinforcing material before the step ofinfiltrating the fill material.
 20. A method of forming and assemblingmetal and ceramic parts, comprising the steps: a. forming at least twoparts using powder metallurgy and/or ceramic forming techniques in amanner that leaves a network of interconnecting porosity in each part,said parts having different coefficients of thermal expansion; b.sintering each formed part; c. assembling the sintered parts together;d. causing a fill material to be infiltrated into the assembled parts;and e. curing the parts and fill material.
 21. The method of claim 20,wherein the step of sintering results in the parts having approximatelyforty percent density and being approximately sixty percent open. 22.The method of claim 20, wherein the fill material is molten metal. 23.The method of claim 20, wherein the fill material is an epoxy.
 24. Themethod of claim 20, wherein the fill material is a thermoset.
 25. Themethod of claim 20, further comprising placing a fiber reinforcingmaterial between the sintered parts during the step of assembling thesintered parts.
 26. The method of claim 20, further comprising wrappingat least a portion of the assembled parts with a fiber reinforcingmaterial before the step of infiltrating the fill material.
 27. A methodof forming and assembling at least two parts together, comprising thesteps: a. forming at least two parts from an alloy-proportionatequantity of elements that raise the eutectic melting point of the alloyin a manner that leaves a network of interconnecting porosity in eachpart; b. sintering each formed part; c. assembling the sintered partstogether; d. melting a fill material comprising an alloy-proportionatequantity of elements that lower the eutectic melting point of the alloyand causing the melted fill material to infiltrate into the assembledporous parts; and e. holding the temperature of the assembled parts atelevated temperature for a predetermined time, causing the fill materialto diffuse a predetermined depth into the surface of the sintered parts.28. The method of claim 27, further comprising placing a fiberreinforcing material between the sintered parts during the step ofassembling the sintered parts.
 29. The method of claim 27, furthercomprising wrapping at least a portion of the assembled parts with afiber reinforcing material before the step of infiltrating the fillmaterial.
 30. A method of assembling two or more parts comprising thesteps: a. forming at least two separate parts comprised of metal foamand /or ceramic foam; b. assembling the parts; c. causing a fillmaterial to be infiltrated into the assembled parts; d. curing the partsand fill material.
 31. The method of claim 30, further comprisingplacing a fiber reinforcing material between the parts during the stepof assembling the parts.
 32. The method of claim 30, further comprisingwrapping at least a portion of the assembled parts with a fiberreinforcing material before the step of infiltrating the fill material.33. A method of assembling two or more parts comprising the steps: a.forming at least two separate parts comprised of perforated metal and/orperforated ceramic; b. assembling the parts; c. causing a fill materialto be infiltrated into the assembled parts; and d. curing the parts andfill material.
 34. The method of claim 33, further comprising placing afiber reinforcing material between the parts during the step ofassembling the parts.
 35. The method of claim 33, further comprisingwrapping at least a portion of the assembled parts with a fiberreinforcing material before the step of infiltrating the fill material.